1. Field of the Invention
The present invention relates to wireless communication and, more particularly, to a method and apparatus for detecting space-time block codes.
2. Related Art
Schemes using a plurality of transmission/reception antennas include a spatial multiplexing scheme and a space-time coding scheme. The spatial multiplexing scheme such as a vertical bell laboratory space-time (V-BLAST) and the like is a scheme of simultaneously transmitting independent data signals through different transmission antennas. A receiver of a V-BLAST system employs detection schemes using QR decomposition of an equivalent space-time channel matrix, and a DF (Decision Feedback) algorithm, an ML (Maximum Likelihood)/DF algorithm obtained by combining ML and DF algorithms, a PD (Parallel Detection) algorithm, p-PD algorithm, and the like, are representative detection schemes. Korean Patent Registration No. 10-0659281 may be referred to in relation to definitions, content, and the like, of the detection schemes including the p-PD algorithm. The DF algorithm based on interference nulling and interference cancellation is very simple but causes a severe performance degradation due to error propagation.
In the ML/DF algorithm, first some transmission layers are detected by using the ML algorithm and the other remaining layers are detected by using the DF algorithm. Thus, reliability of data symbols used in the interference cancellation process can be improved.
In the PD algorithm, one layer called a candidate layer is first selected and the DF algorithm is applied to the other remaining layers with respect to each of candidate symbols of the candidate layer, thereby improving performance compared with the DF algorithm. A candidate symbol vector that minimizes Euclidean distance between candidate symbol vectors and reception vectors obtained from the process is selected to thus make a final decision.
The p-PD algorithm, an extended PD algorithm, is selecting two or more candidate layers. The PD algorithm provides performance close to that of the ML algorithm while having a rational detection complexity over up to four transmission antennas. However, the PD algorithm shows a severe performance degradation with an increased number of antennas. Thus, in order to maintain the ML performance, the p-PD scheme using two or more candidate layers is required. However, the use of more than two candidate layers results in a considerable increase in the detection complexity.
Meanwhile, the space-time coding scheme is a method of applying coding to a time axis and a space axis in order to obtain both spatial diversity and coding gain. Space-time block codes (STBCs) having orthogonal characteristics based on an orthogonal design theory have been proposed as a scheme for obtaining an optimum transmission antenna diversity gain. These orthogonal STBCs (O-STBCs) have a maximum diversity order and have an advantage in that it can detect a maximum likelihood even by simply performing linear processing at a reception end. In case of an STBC without having such a special structure as orthogonality, its complexity of maximum likelihood detection increases at the ratio of arithmetical (geometrical) progression over a modulation order Q and the number N of transmission antennas.
Recently, there has been an attempt to apply the DF algorithm to an STBC detection, which, however, involves a severe performance degradation compared with the ML detection. In order to obtain performance close to that of the ML algorithm, a sphere decoding (SD) scheme has been applied to the STBC detection. Besides, the SD algorithm, the V-BLAST detection algorithms such as the PD and p-PD algorithms can be also applicable to an STBC system having an equivalent space-time channel matrix. The PD algorithm causes a slight performance loss compared with the ML detection, whereas the p-PD algorithm provides the substantially same performance as that of the ML detection. However, although the detection complexity of the PD and p-PD algorithms is significantly low compared with the ML detection, it is still too high to be implemented over a large modulation order.